1. Field of the Invention
The present invention relates to an image forming apparatus and a computer readable recording medium.
2. Description of Related Art
Image processing apparatuses such as a printer, MFP (Multi Function Peripheral) and the like which carry out printing by receiving print data such as PS (PostScript (registered trademark)) data, PDF (Portable Document Format) data and the like created in an external apparatus such as a PC (Personal Computer) and the like via a network such as LAN, converting the received data to data of intermediate format (intermediate data) temporarily and generating bitmap data by rasterizing the intermediate data is becoming widely used.
In such image processing apparatus, in order to reduce memory capacity, print data of one page is divided in a plurality of bands when converting the print data of the page to intermediate data, bitmap data is generated in band unit based on the intermediate data and the bitmap data is sequentially transmitted upon request by an image forming unit which carries out image forming.
Here, processing time needed for rasterizing depends on a level of complication of the intermediate data. Further, because transmission of bitmap data needs to be executed at every predetermined time along with forming of an image in the image forming unit, the transmission of bitmap data cannot be carried out at the timing requested by the image forming unit when the processing time needed for rasterizing is too long and missing of image (overrun) occurs.
That is, for example, as shown in FIG. 22, print data of one page is converted to intermediate data such as a display list and this intermediate data is divided in a plurality of bands. As for the first band B1 to the fourth band B4 among the divided bands, rasterizing can be completed before the timing (t1 to t4) requested by the image forming unit and bitmap data can be transmitted. However, as for the fifth band B5, the intermediate data is complicated and rasterizing cannot be completed in time for the timing requested by the image forming unit, and bitmap data cannot be transmitted. In such case, an image of the object in which rasterizing is not completed will be missing.
In view of the above problem, among conventional image processing apparatuses, JP H10-307689 discloses an image processing apparatus which estimates rasterizing time for each band at the time when analyzing input data. Further, the above image processing apparatus restructures the construction of the intermediate data or carries out rasterizing in page unit for the band which is determined that rasterizing cannot be finished in time for the timing requested by the image forming unit to prevent overrun from occurring.
Moreover, JP2003-51019 discloses an image processing apparatus which attempts to enhance processing capacity by carrying out rasterizing in parallel in a plurality of bands by using a plurality of CPU.
However, in the image processing apparatus described in the above JP H10-307689, the process is increased when the intermediate data is restructured and rather decreases image forming speed. Further, when it is changed so as to carry out rasterizing in page unit, cost increases because a memory region for storing bitmap data is needed and activation of the image forming unit will be delayed, therefore, again, image forming speed will be decreased.
Moreover, in the image processing apparatus described in the above JP2003-51019, speed of rasterizing can be enhanced, however, because image forming speed in the image forming unit is constant, the performance will not be enhanced even when rasterizing can be carried out before the timing requested by the image forming unit more than needed. In contrary, a memory region for storing the bitmap data which is generated too early is needed and as a result, cost increases.